I am curious to know what stale beer really tastes like. For me I can read about what certain off flavors are supposed to taste like. However, taste and flavor can be so subjective its hard to really now until someone says; "Here, this is really stale."

So I was wondering if anyone knew the best way to maybe force stale a beer in a closed bottle? Or how best to doctor a beer to get it to stale after opening?
What is stale beer supposed to taste like?

EDIT: Are there any BJCP instructors on-line here that can speak to how the BJCP trains judges to pick out oxidation?

I think you can taste "stale" in hoppy beers that have been sitting around for a while. It's definitely a matter of personal opinion, but try a super hoppy beer the day it comes off the line, and try one after its been on the shelf for a few months. A great example of this is 90 minute. Or, to try at home, dry hop a pale ale or IPA, and let it sit in secondary for a few months.

I had a brewdog beer last night. I assume it was shipped on a freightor. The Best by date is tomorrow. That beer was stale. Just lifeless. You could just miss treat an IPA as you bottle it, get some oxygen in there. It'll taste stale after a few months.
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Tim WeberMar 3 '10 at 18:18

I'm a BJCP judge who teaches judge training classes. One way we teach off flavors is to use a kit to doctor other beers. Staling can take a few different forms. The most common, oxidation, is often described as a "wet cardboard" flavor and aroma, which is pretty accurate. Another clue to staling is darkening of the beer, or a kind of weird caramel aroma and flavor.

Open a package of unsalted saltines and leave it on top of the refrigerator.

Once your package arrives, enjoy your purchase.

Cut a 2 inch square piece from the cardboard box & soak in warm water for 10 minutes.

Remove the wet cardboard and pat dry.

Break up stale saltines and sprinkle on top of the damp cardboard.

Serve.

All kidding aside, I'm not sure how to make your beer stale without opening the package. You could possibly get this effect by aerating a few bottles at packaging time. Oxygen is one of the spoiling agents. Or find a beer made overseas - a British ale would be my first choice. Time and oxygen are the enemies here.

The adventurous can spend money to buy off-flavors which they put in perfectly good beer.